The invention relates to an inking unit for a printing machine, which is assigned to a printing form and includes a first distributor roller and a second distributor roller.
An inking unit of this general type is described in the published German Patent Document DE 30 34 644 C2 and, in addition to the distributor rollers, also includes oscillating ink applicator or inking rollers. The frequency of the axial oscillation of one of the ink applicator rollers is slightly higher than the frequency of the axial oscillation of the distributor roller against which the one ink applicator roller bears. That ink applicator roller within a roller train, which is disposed closer to the printing form, therefore, oscillates faster than the distributor roller disposed farther away from the printing form.
An inking unit is likewise described in the published German Patent Document DE 298 12 966 U1 as including a first distributor roller and a second distributor roller. Furthermore, the inking unit includes a third distributor roller and a bridge-type roller, which is simultaneously in rolling contact with an ink applicator roller of the inking unit and a dampening-solution applicator roller of a dampening unit and oscillates at a distribution frequency of 1:8. The first distributor roller has a distribution frequency of 1:6 and oscillates more slowly than the second distributor roller and the third distributor roller, each of which oscillates at a distribution frequency of 1:4 and is disposed closer to a plate cylinder than the first distributor roller.
It is accordingly an object of the invention to provide an improved inking unit of the general type mentioned at the introduction hereto.
With the foregoing and other objects in view, there is provided, in accordance with one aspect of the invention, an inking unit for a printing machine, which is assigned to a printing form, comprising a first distributor roller and a second distributor roller, the first distributor roller being in rolling contact simultaneously with two ink applicator rollers, and being axially oscillatable more slowly and disposed more closely to the printing form than is the second distributor roller.
In accordance with another feature of the invention, the second distributor roller is axially oscillatable twice as quickly as the first distributor roller, so that a ratio between frequencies of oscillations of the two distributor rollers is 1:2.
In accordance with a further feature of the invention, a ratio between frequencies of the axial oscillations of the two distributor rollers is 1:3.
In accordance with an additional feature of the invention, the second distributor roller is disposed more closely to an ink duct than is the first distributor roller.
In accordance with a concomitant aspect of the invention, there is provided a printing machine having a printing form and an inking unit, comprising a first distributor roller and a second distributor roller, the first distributor roller being in rolling contact simultaneously with two ink applicator rollers, and being axially oscillatable more slowly and disposed more closely to the printing form than is the second distributor roller.
Thus, the object of the invention is achieved by an inking unit having a first distributor roller in rolling contact simultaneously with two ink applicator rollers, the first distributor roller being axially oscillatable more slowly and being disposed more closely to a printing form than is the second distributor roller.
The fact that, in the inking unit according to the invention, the first distributor roller is disposed closer to the printing form than is the second distributor roller, and a frequency of the axial oscillation of the first distributor roller is lower than a frequency of the axial oscillation of the second distributor roller, while the two distributor rollers oscillate simultaneously during printing operation, results in various advantages: the slow oscillation of the first distributor roller is advantageous with regard to reducing an ink gradient on the printing form. By an ink gradient, it is understood to mean a reduction in the ink layer thickness or ink density from the printing start to the printing end. The closer the first distributor roller is located to the printing form, i.e., the fewer the rollers of a roller train are located between the first distributor roller and the print form, the more effective the first distributor roller acts with regard to reducing the ink gradient. There is preferably only a single roller in the roller train between the first distributor roller and the printing form, specifically an ink applicator roller, against which the first distributor roller bears.
Rapid oscillation of the second distributor roller is advantageous with regard to eliminating ink-free strips, which are caused by supporting webs of metering elements of an ink metering system on an ink-duct roller belonging to the inking unit.
The mutually different frequencies of the axial oscillations of the two distributor rollers are additionally also advantageous with regard to the elimination of ghosting effects.
In an advantageous development of the inking unit according to the invention, the second distributor roller oscillates in the axial direction three times as quickly as the first distributor roller, so that the ratio between the frequencies of the oscillations of the two distributor rollers is 1:3. In other advantageous developments, the ratio between the frequencies of the axial oscillations of the two distributor rollers is 1:2 or 2:3.
In the event that the inking unit is equipped with an ink duct which, as an ink metering duct, is equipped with the ink metering system, the second distributor roller within the roller train can be disposed closer to this ink duct and therefore to the ink metering system than is the first distributor roller. The roller train, to which the first distributor roller and the second distributor roller can jointly belong, is a chain of rollers which roll on one another and, as a result, convey the printing ink from the ink metering system to the printing form.
Other features which are considered as characteristic for the invention are set forth in the appended claims.
Although the invention is illustrated and described herein as embodied in an inking unit, it is nevertheless not intended to be limited to the details shown, since various modifications and structural changes may be made therein without departing from the spirit of the invention and within the scope and range of equivalents of the claims.
The construction and method of operation of the invention, however, together with additional objects and advantages thereof will be best understood from the following description of specific embodiments when read in connection with the single figure of the drawing, wherein: